NEW YORK (CNN/Money) – In the State of the Union address Wednesday evening, President Bush answered some important questions about his plans for Social Security reform and the creation of individual investment accounts. Many issues remain unclear, however.

Here are some of the topics Bush addressed and some further details from a fact sheet on his proposal.

Would reform affect everyone? The president has said all along that any reform would not affect the benefits of current and near retirees. On Wednesday, he specified that benefits of anyone age 55 and older will not be changed.

Who could open an investment account? The accounts are voluntary. But participation would be phased in over three years according to age. In the first year -- 2009 -- workers born from 1950 to 1965 could open accounts. In the second year, workers born from 1950 to 1978 could open accounts. In the third year, anyone born after 1950 could opt for an account.

How much payroll tax would be diverted to individual investment accounts? President Bush indicated that eventually, workers would be permitted to invest up to a third of the 12.4 percent payroll tax that they and their employers pay on their wages. (Workers pay 6.2 percent and their employers pay the other 6.2 percent.)

Annual contributions would be capped at $1,000 in 2009 and thereafter rise slightly more than $100 per year.

How would we pay for the costs of creating individual investments accounts? Payroll taxes are used to pay current retirees, so diverting a portion of them creates a shortfall in the ability to pay full benefits.

The transition costs of diverting a third of payroll taxes to individual investment accounts have been estimated at around $2 trillion over the next 10 years. That assumes, though, that a third of payroll tax is diverted for each of the 10 years.

The White House in December indicated the government would borrow the money to make up for that shortfall. But on Wednesday, the president didn't mention that.

Instead, he said the diversion of tax to individual accounts wouldn't be abrupt. Bush recommended "starting personal retirement accounts gradually and raising the yearly limits on contributions over time, eventually permitting all workers to set aside four percentage points of their payroll taxes in their accounts."

That would lessen the immediate impact on the U.S. budget by somewhat reducing the transition costs, said Ron Gebhardtsbauer, senior pension fellow at the American Academy of Actuaries.

How would individual accounts work? The accounts would be modeled on the Thrift Savings Plan -- a 401-k type program that is already available to government employees -- and centrally administered by the government.

Workers would have a choice of five broadly diversified index funds and a lifecycle fund, in which the portfolio grows more conservative as the investor nears retirement.

"We will make sure there are good options to protect your investments from sudden market swings on the eve of your retirement," the president said in his speech. Specifically, when a worker turns 47 the account will automatically be invested in the lifecycle fund unless the worker and his or her spouse sign a waiver opting out.

In terms of fees, the Social Security Administration estimates the administrative cost per account will be 0.3 percentage points.

Money in the accounts could not be taken out or borrowed before retirement. At retirement, it's likely workers would have to annuitize a portion and only take out a lump sum if doing so would not result in the worker moving below the poverty line. Any unused portion of the account could be left to heirs.

What other options would the president consider to make Social Security solvent? President Bush again ruled out increasing the payroll tax -- which is 12.4 percent of one's wages up to a certain cap ($90,000 this year). But in his remarks Wednesday he said, "fixing Social Security permanently will require an open, candid review of the options. ... I will work with members of Congress to find the most effective combination of reforms."